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A053067 a(n) = concatenation of next n numbers (omit leading 0's). 25
1, 23, 456, 78910, 1112131415, 161718192021, 22232425262728, 2930313233343536, 373839404142434445, 46474849505152535455, 5657585960616263646566, 676869707172737475767778, 79808182838485868788899091, 9293949596979899100101102103104105, 106107108109110111112113114115116117118119120 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Concatenation of the integers from A000124(n-1) up to and including A000217(n). - R. J. Mathar, Aug 30 2013

The second term is a prime. When is the next prime, if there is another? - N. J. A. Sloane, Dec 16 2016

REFERENCES

Felice Russo, A set of new Smarandache functions, sequences and conjectures in number theory, American Research Press 2000.

LINKS

Table of n, a(n) for n=1..15.

FORMULA

a(n) = n^2/2 + n/2 + Sum_{k=1..n-1} (n^2/2 + n/2 - k)*10^Sum{j=0..k-1} floor(1 + log_10(n^2/2 + n/2 - j)). - Paolo P. Lava, Dec 16 2008

MAPLE

P:=proc(i) local a, k, j, n; for n from 1 by 1 to i do a:=n^2/2+n/2+sum('(n^2/2+n/2-k)*10^sum('floor(1+evalf(log10(n^2/2+n/2-j)))', 'j'=0..k-1)', 'k'=1..n-1); print(a); od; end: P(100); # Paolo P. Lava, Dec 16 2008

MATHEMATICA

Table[FromDigits[Flatten[IntegerDigits/@Range[(n(n-1))/2+1, (n(n+1))/2]]], {n, 20}] (* Harvey P. Dale, Jan 23 2016 *)

PROG

(PARI) a(n) = my(s = ""); for (i=n*(n-1)/2 + 1, n*(n+1)/2, s = concat(s, Str(i)); ); eval(s); \\ Michel Marcus, Aug 11 2017

CROSSREFS

A subsequence of A035333. For primes in latter, see A052087.

See A279610 for a variant.

Sequence in context: A001369 A007923 A080479 * A036906 A134733 A095256

Adjacent sequences:  A053064 A053065 A053066 * A053068 A053069 A053070

KEYWORD

easy,base,nonn

AUTHOR

Felice Russo, Feb 25 2000

EXTENSIONS

More terms from James A. Sellers, Feb 28 2000

More terms from Michel Marcus, Aug 11 2017

STATUS

approved

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Last modified October 23 03:21 EDT 2019. Contains 328335 sequences. (Running on oeis4.)